The invention relates to compact circuit packages for electronic circuits including high power applications.
A circuit package typically includes a base plate having an electrically insulative thermally conductive substrate, such as ceramic, bonded thereto. Circuit means, including lead frames and circuit components, are bonded to the substrate. A housing covers the base plate, substrate and circuit means. The other side of the base plate is typically mounted against a heat sink.
Though not limited thereto, the invention particularly arose from efforts to design a circuit package for high power applications where the base plate is too large for an optimally effective single substrate. In this aspect of the invention, a plurality of electrically insulative thermally conductive separate substrates are bonded on the base plate. The lead frame means is formed from a single unitary integral member which is bonded to the substrates in a single simple operation, such as solder reflow, which also bonds the substrates to the base plate. Portions of the lead frame are bent upwardly and extend outside of the housing for external circuit connection.
Alignment means is provided, including a hole in the lead frame aligned with a hole in the base plate through a gap between the substrates. In one form, pre-bonding alignment is effected by rotating the lead frame about a pin through the alignment holes and the gap between the substrates until the lead frame reaches a designated stop.
The circuit means and the substrates are encapsulated with epoxy or the like. The lead frame has a set of holes aligned with gaps between the substrates therebelow for enabling air bubbles to escape during epoxy encapsulation such that epoxy can flow under the lead frame and between the substrates. The holes also reduce surface tension of the solder or other bonding material, so as to prevent the substrates from sliding together.
In another aspect of the invention, improved design flexibility for high power applications is provided by a plurality of electrically conductive shouldered jumper posts received in respective holes of the lead frames. Jumper bus means are received on the jumper posts for selectively interconnecting designated sections of the circuit means. The jumper bus is spaced above other sections of the circuit means.
In another aspect of the invention, a circuit package is provided with power terminal extensions having an outer end adapted for external circuit connection and having an inner bifurcated end mounted to and receiving a respective terminal portion of the lead frame between the bifurcations. Notches are provided in the lead frame terminal portion edges for locating and aligning respective power terminal extensions. The power terminal extensions have notches at their edges for locking the extensions in the housing and providing additional support for the extensions. The extensions are bonded to the terminal portions of the lead frame by solder or the like. The bifurcations of the inner end of the terminal extensions have one or more holes therethrough for insuring the flow of solder or like bonding material in and around the interface joint of the terminal extensions and the terminal portions of the lead frame.